As alternative power sources for replacing batteries, piezoelectric energy harvesters are designed for the applications which demand low-power electronics and sustainable electrical power. This paper presents the design of a new piezoelectric energy harvester with two-stage force amplification frame for the purpose of harvesting energy from human footstep. The two-stage force amplification frame can magnify the walking force applied to the piezoelectric stack and thereby enhances the power output. Analytical model is established to obtain the relationship between the input and output based on elastic beam theory. The frame parameters are designed and optimized to meet the requirements on low-frequency condition and to achieve the maximum force amplification ratio. Finite element analysis is conducted to verify the performance of the proposed frame.